Laura Creighton wrote:
In a message of Tue, 15 Sep 2009 19:41:25 BST, Paul Moore writes:
MAL pointed out http://code.activestate.com/recipes/573441/ - extended
optparse to allow definition of required options. Given that one of
the requirements that argparse is claimed to meet where optparse
doesn't is supporting required arguments, how come this simple recipe
hasn't been incorporated into optparse?
The optparse/argparse case seems to rest on the argument that optparse
cannot be extended to do what argparse does. It seems like this isn't
true for all requirements. (And maybe some others could be addressed
by judiciously deprecating support for specific internal details that
maybe should not have been documented in the first place...)
Maybe, but this simple recipe only works for options which are
unconditionally required. What I needed was a solution for options
that are conditionally required -- if you have option X then you
must have option Q.
But optparse is particularly unhappy about this, and about other
things. If you type command --verbose --brief, and these are
toggles, then you will get the last one processed, brief in this
case. There is no easy way to say 'now please roll over and die'
because you have an incompatible set of options. I wrote code
that changed optparse to do what I wanted, but boy, was it ugly.
I can maybe dig it up somewhere. And when I went knocking, asking
optparse's author about how he would recommend that I solve my
problem using optparse in a way that was less ugly, I was told
that my problem wasn't to be solved using optparse.
So I would surmise that the reason this recipe isn't in the standard
library is optparse's author didn't want it in optparse.
Plus, more useful than required options are required positional
arguments - which optparse doesn't handle at all (and exposes features
that makes handling them difficult to do in a backwards incompatible way).
Required options are easy to do yourself - just check for their presence
and error out if they aren't there. It is the other features that are
more difficult.
Michael
Paul.
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